The invention relates generally to electronic amplifiers which use field-effect transistors, and relates more particularly to those using MOSFET (metal oxide silicon field effect transistors).
Individual MOSFET devices can be connected as amplifiers in various known ways e.g. common source, common gate, common drain, source follower, etc. to provide different characteristics of operation as desired to suit a particular purpose. Two such devices can also be connected together to provide a variety of possible input and output characteristics which are not obtainable with just one device. One example of this in the commonly used "cascode" configuration, in which a first-stage device is connected in a common-source configuration, with its output going to the input of a second device connected in a common-gate configuration. The resulting structure is an amplifier having a high input impedance, low noise, and a high gain.
When a pair of MOSFET devices is connected to provide amplification, the gate of one of the devices must generally be provided with a bias voltage in order that the drain-to-source voltage of the other device will be sufficiently high to put that other device into an active operating condition in which it exhibits significant gain. The need for such bias voltage usually requires a voltage generator network on the same chip. The requirement for this network leads to increased circuit complexity and degrades the performance of the amplifier in several respects.